1 October 2012

Tea and coffee break.
‘Whether hot or cold, strong or weak, black or green, sweet or smoky, oolong or pekoe, with milk or lemon, bag or leaf, tea is the universal drink of countless millions.’ – Tea: A global history, Reaktion Books. We asked Glenn Cardwell to bring us up to date on recent studies and the benefits of taking a tea or coffee break. The following piece, reproduced with permission, first appeared on Glenn’s blog.

Glenn Cardwell

‘Humans have enjoyed tea and coffee for quite some time. Coffee was being drunk in Europe in the mid-17th century, while tea was supposedly consumed by the Chinese 4500 years ago, although this strongly disputed as the first mention of tea in a Chinese text was only 2000 years ago. Tea arrived in Europe around the same time as coffee.

The news is good I have said good things about tea and coffee over the years because I prefer a positive food story rather than the scare stories enjoyed by others. It is always comforting to have science on your side. A recent meta-analysis crunched all the research papers between 1966–2011, which included 140,000 coffee drinkers and came to the conclusion: “Moderate coffee consumption is inversely associated with the risk of heart failure, with the largest inverse association observed for consumption of 4 servings per day.” And it didn't matter whether you’re a boy or a girl. With 4 cups of coffee a day there was a 11% lower risk of heart failure. Any benefit was negated once you reached 10 cups a day. The analysis took account of body weight, alcohol consumption and smoking, as is always the way in making sense of research.

And then it gets better Some scientists who live just down the road from me at the University of Western Australia took a look at both tea and coffee and the potential risk of heart disease. They too were positive about a lower risk of heart disease in tea and coffee consumers after reviewing the published evidence. Tea seemed to improve the normal functioning of the arterial walls, lower triglycerides, inhibit inflammation and LDL-cholesterol oxidation (the latter two significantly contribute to atherosclerosis) and even lower the risk of stroke. Both tea and coffee are associated with a lower risk of type 2 diabetes. The association seems to be strongest with coffee, possibly due to the chlorogenic acids in coffee.

How much tea and coffee? Difficult to say precisely, but there is general agreement that 3–5 cups a day is having a useful effect on your health. They did emphasise that your genes could be playing an important role, meaning we can’t say that everyone will benefit from tea and coffee. For example, those with the polymorphism CYP1A2 in the P450 enzyme (that's laboratory clever people talk I think) are slow caffeine metabolisers, and actually have a higher risk of a heart attack with caffeinated drinks. All the same, it sounds very encouraging to me.

Is there a “yes, but”? Isn’t there always? Generally, the studies rely on self-reported tea and coffee consumption and only one point in time. If you believe that tea and coffee are “bad” then you will probably fib about how much you guzzle, and often people just plain “forget” how much they drink and therefore under-report. Or they may have changed drinking habits over time depending upon what they read in the paper. Association is not necessarily cause and effect. It could also be that the folk enjoying a brew three or four or five times a day might also eat more vegetables, watch only documentaries, cook proper meals, help their neighbours, give to charity, walk the dog and hug the kids. Nevertheless, when the numbers are given a thorough massage, it looks like moderate tea and coffee drinkers come out ahead in the health stakes,

1939 poster from the Empire Marketing Board

What does it all mean? If you drink tea or coffee, feel very comfortable with the habit. All the evidence suggests that up to 5 cups a day is fine and may even be a generous leg-up for your health. I suspect that even – 8 cups a day is OK. Twenty cups? I’m not so sure. Maybe worth considering a cut back. No-one is certain what specific compounds in tea and coffee are responsible for their proposed protection. There are many biologically active compounds, both known and unknown, in tea and coffee. Between you and me, 6 cups of tea a day find their way down my throat. They are big cups and I ain’t worried in the slightest. Hopefully, before I die, science will reveal why tea helped me live to 105.’